1. Field of the Invention
The present invention relates to phased array radar system, and more particularly to signal time delay devices which include magnetostatic spin wave elements used to time delay the transmitted signals.
2. Description of the Prior Art
Present day phased array radar antennas are electronically steered by a phase shifting circuit element in each radiating element of the array.
For steering purposes an emitted signal is subjected to a phase shift of no more than 2.pi. radians as provided by each phase shifting circuit element. However, many of these phased array radar antennas are physically tens of feet across. A waveguide signal feed system which feeds, or provides a signal for each radiating element of the array, driven by a signal generated by an oscillator would comprise a multiplicity of waveguides of varying length dependent upon the location of the emitting element. The location of the radiating or emitting element would determine the length of the waveguide feed. Thus, the signal transit time from the oscillator generating the signal through the multiplicity of individual waveguides to the variously located radiating or emitting elements of the antenna array would not be constant across the array. The leading and trailing edges of a transmitted pulse would suffer signal degradation because not all of the elements are illuminated at the same time for these leading and trailing edges.
Present solutions to this problem of variable signal transit time involve the addition of phase shifts of multiples of 2.pi. to the antenna system. This addition of 2.pi. of phase shifting creates beam steering through the control of a relatively small phase angle of 2.pi. radians on top of a fixed but greater signal shift of 2n.pi. radians, where n is an integer.
A paper authored by V. B. Anfinogenov, T. N. Verbitskaya, P. E. Zil'berman, G. T. Kazakov and V. V. Tikhonov entitled "Propagation of Magnetostatic Waves in a Ferrite-Ferroelectric Structure", published in The Soviet Technical Physics Letters, 12 (4), April 1986, describes the change in group velocity in a magnetostatic wave (MSW) when a ferrite supporting the wave is placed into contact with a ferroelectric material. However, the practical application of this device as a time delay device was not described.
The problem to be solved therefore is the equalization of signal transit times in the feed lines of phased array antennas by adjustable time delay instead of through 2.pi. phase shifters.